<template>
    <ul class="list">
        <li class="item"
            v-for="item of letters"
            :key="item"
            :ref="item"
            @touchstart.prevent="handleTouchStart"
            @touchmove="handleTouchMove"
            @touchend="handleTouchEnd"
            @click="handleLetterClick"
        >{{item}}</li>
    </ul>
</template>

<script>
    export default {
        name: 'CityAlphabet',
        props:{
            cities:Object,
        },
        data(){
            return{
                touchStatus:false,
                startY:0,
                timer:null
            }
        },
        computed:{
            letters(){
                const letters=[]
                for(let i in this.cities){
                    letters.push(i)
                }
                return letters
            },
        },
        updated () {
            this.startY = this.$refs['A'][0].offsetTop
        },
        methods:{
            handleLetterClick(e){
                console.log(e.target.innerText)
                this.$emit("change",e.target.innerText);
            },
            handleTouchStart(){
                this.touchStatus=true
            },
            handleTouchMove(e){
                if(this.touchStatus){
                    if (this.timer) {
                        clearTimeout(this.timer)
                    }
                    this.timer = setTimeout(() => {
                        const touchY = e.touches[0].clientY -this.startY
                        const index = Math.floor((touchY - this.startY) / 20)
                        if (index >= 0 && index < this.letters.length) {
                            this.$emit('change', this.letters[index])
                        }
                    }, 16)
                }
            },
            handleTouchEnd(){
                this.touchStatus=false
            }
        }
    }
</script>

<style lang="stylus" scoped>
    @import "~@/assets/Styles/varibles.styl"
    .list
        display: flex
        flex-direction: column
        justify-content: center
        position: absolute
        top: 1.58rem
        right: 0
        bottom: 0
        width: .4rem
        .item
            line-height: .4rem
            text-align: center
            color: $bgColor
</style>

